Move `REFUND_AUTH_PER_EXISTING_ACCOUNT` and `TX_MAX_GAS_LIMIT` with other gas constants

This is a gas thing. Should it be moved as well?

_Originally posted by @SamWilsn in https://github.com/ethereum/execution-specs/pull/2396#discussion_r3075550303_
            
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Why not this one?

_Originally posted by @SamWilsn in https://github.com/ethereum/execution-specs/pull/2396#discussion_r3075586793_
            